Development of a Cobalt Electrode for the Determination of Phosphate in Soil Extracts and Comparison with Standard Methods

Abstract

7A phosphate-sensitive cobalt electrode was evaluated in detecting orthophosphate 8 ions (H 2 PO 4 − ) in ammonium lactate-acetic acid soil extracts. The dependence of the 9 mixed potential of a cobalt electrode on H 2 PO 4 − concentration was investigated via 10 potentiometry. The mechanism of detection is based on the consumption of a 11 surface cobalt (II) oxide layer to form (Co 3 (PO 4 ) 2 ), which leads to a concentration-12 dependent shift of the mixed potential. Two reference electrodes were evaluated: 13 Ag/AgCl (3 M) KCl and a platinum (Pt) wire. A linear response was observed using 14 both reference electrodes. However, application of a Pt wire quasireference 15 electrode increased the linear dynamic response range of the detector from 10-10 3 16 mg L -1 or 10 −4 -10 −1 M (Ag/AgCl (3 M) KCl) to 0.1-10 5 mg L -1 or 10 −6 -10 1 M. In 17 addition, the response time using the Pt wire was less than 5 minutes compared to a 18 minimum of 10 minutes using Ag/AgCl (3 M) KCl. There was close agreement 19 between the response of the phosphate-sensitive cobalt electrode with a standard 20 colorimetric method. As dissolved organic substances can potentially interfere with 21 electrochemical techniques, an investigation into the use of a nonpolar resin for 22 decolorization and removal of organic matter in soil extracts was carried out and 23 successfully employed. The phosphate-sensitive cobalt electrode was found to be a 24 fast method for the analysis of soil extracts with high sensitivity and selectivity. It has 25 the potential to be developed into a sensor for the in situ measurement of phosphate 26 in various environmental matrices. 27 28 Warwick et al. 2013). In soil extracts (water and 36 dilute salt solutions such as KCl and CaCl 2 ), P is usually found in the form of the 37 orthophosphates H 2 PO -4 and HPO 2-4 (0.01 -3.0 mg L -1 ) (Sims 2000; Warwick et al. 38 2013), which are the main readily available forms of P for plant growth. In rivers, 39 orthophosphate concentrations vary greatly from 0.02 -1 mg L -1 . (Quintana et al. 40 2004; Warwick et al. 2013). In natural and waste waters orthophosphate 41 concentration varies from 0.2 -10 mg L -1 , while in soil it varies from 0.2 -50 mg kg -42 1 (Warwick et al. 2013). In recent decades, a large increase in the use of phosphate-43 containing fertilisers has resulted in increased concentrations of orthophosphate in 44 land runoff, which can lead to eutrophication. This process is regarded as one of the 45 major threats to the aquatic environment (Abowei et al. 2005). Thus, there is a need 46 for the development of improved orthophosphate detection techniques in order to 47 enhance our knowledge regarding the major sources of orthophosphate input to 48water bodies and to improve our understanding of P-cycling in various environments. 49The methods used for the monitoring and management of environmental P, based 50 on its accurate determination in soil and water samples, were reviewed by Worsfold 51 et al (2005). Most often the Murphy and Riley (1962) colourim...

Multivariate Standard Addition Cobalt Electrochemistry Data Fusion for Determining Phosphate Concentration in Hydroponic Solution

“…The highest determination coefficient (R 2 ) of the linear regression model was 0.71, which is similar the results obtained in previous studies [35], which reported a high possibility of alteration in oxidation layer (CoO) formation on the cobalt electrodes. To combat this issue, a buffering solution is used to maintain the oxidation layer over a long period [53] or the normalization is used based on two, three, or even multiple points. However, this needs to keep prepared the standard solution at all times for fitting the nonlinear data [54], which is a disadvantage of this method.…”

A Co-Nanoparticles Modified Electrode for On-Site and Rapid Phosphate Detection in Hydroponic Solutions

“…In order to ensure the repeatability and reproducibility of sensor data. Statistical differences among means were evaluated using Student’s t-test, ANOVA-single factor, and F-test at a 95% confidence interval ( p < 0.05) [ 32 , 33 ].…”

Recent Advances in Chemical Sensors for Soil Analysis: A Review

“…− detection [77]; and applications based on the transformation of Co(H 2 PO 4 ) 2 to CoO and/or Co(OH) 2 on cobalt wire electrodes [78]. A disposable on-chip micro-sensor with planar cobalt (Co) microelectrodes and an Ag/AgCl reference for phosphate detection in soil extracts was reported by Zou et al [79].…”